(Djot) Bad priority between alpha- and roman-numbered list items

[Omikhleia]

Djot input:

i. ddd
i. ddd

Observed = interpreted as an alpha list:

i. ddd
j. ddd

Workaround to get roman numbers:

i. ddd
ii. ddd

Nevertheless we need to prioritize roman numerals over alpha-numbering when ambiguous: djot.js was already fixed that way.

See jgm/djot.lua#7 (not yet merged at the time of writing) --> Check if it does the trick and consider backporting it into our vendored local copy of djot.lua.

[Omikhleia]

I actually used the workaround in the documentation, but had forgotten about it:

https://github.com/Omikhleia/markdown.sile/blob/main/examples/sile-and-djot.dj#L93-L94